"I would like to study those water bears myself.
What kind of microscope do I need?"

At first sight this sounds like a simple question. But when looking around the web you will find lots of complicated discussions referring to microscope equipment.
In order to explain the task, we have scanned an area of about 1 cm² by means of a consumer flatbed scanner equipped with a transparancy unit:

Red Echiniscus tardigrades in a flat water droplet.
Overall surface area: 1 cm².
The dots of the grid define
0.1 cm x 0.1 cm squares. The legs of the water bears and their stomachs - with some dark vegetable material included - are clearly visible but there are no further details.
Image taken by means of an "Epson Perfection 2450 Photo" flatbed scanner using the transpareny unit; optical resolution 2400 dpi.

As you will admit, the scanner performs fair but, of course, has no chance to compete with a microscope. Tardigrades with a body length of 0.3 mm and less are barely noticeable.
So-called Eutardigrades, i.e. colourless tardigrades without "hairs" and armour plates, like  Milnesium tardigradum   are bigger, typically 0.5 mm to 0.7 mm in length, some even reaching 1 mm. In those cases the scanner would reveal a little bit more detail. But still, we will not be able to get more information than with a 10x magnifying glass. See example of a magnifying glas image in  issue #2.

The bare human eye, though of course a miracle by itself, performs only weakly in the macro range. It has an optical resolution of about 0.12 mm at best (KREMER 1984). So it should be able to distinguish two image points when there is a distance of at least 0.12 mm between them.
As a consequence a 0.3 mm water bear will be represented by just one or two pixels. No wonder that under those circumstances all tiny animals had a fair chance to be considered as 'worms'. Without microscopes we would have still two worlds: Man's world and tardigrades world - not interfering with each other.

Just think about those point-like tiny red mites which you can perceive sometimes in moments of relaxed idleness, when looking at sun-lit walls and stones - they are small too, but still much bigger than the water bears.

The table below shows three microscopes in the very-cheap-to-modestly-priced market range and what a water bear would look like when seen through those instruments. The links in the left column refer to more detailed descriptions of those instruments.

Conclusions

Many amateurs have started with an instrument similar to the toy microscope. Later on they will have changed to better instruments. When looking around the web you will find many statements strictly suggesting to avoid those toy microscopes. But you will have to admit that even the 10 US $ toy instrument reveals more detail than just those two pixels discussed above, more than the computer scanner and more than the "just a tiny worm" visual impression.

On the other hand powerful optical equipment has become affordable, some of it is in the price range of really dumb electronic toys or of a candlelight dinner. So, feel free to make use of this lucky coincidence that you are living and actively alive in the 21st century. Just think about those who were not that lucky  according to the famous microscopist, astronomer, wife and mother, the Honourable  Mrs. Ward:

"For at that time when I wrote my book, good microscopes were in the hands only of the few."

Beginners should look out for an instrument with standardized threads and objectives like those mentioned in the discussion of the  Tasco microscope. 
A condenser is advisable for higher magnifications and for an optimum use of the available light. Electrical illumination is fine and first choice for work at home. On the other hand electrical power outlets might be not available outside, e.g. on top of a mountain ;-)

An "always-horizontal" object table like that of the Tasco microscope is a big advantage when you want to screen a petri dish in search for tardigrades. As an amateur you will rarely need higher magnifications. Oil immersion objectives are seldom necessary for tardigrade investigations but you will urgently need low magnifications in order to gain a quick overview.

Many microscopes have a standard equipment with 10x, 45x and 100x objectives. For tardigrades you might be much better off with a set of 3x, 10x, 20x and 60x objectives.

Expensive apochromatic objectives are the best choice for photographic work. For visual inspection good achromatic objectives will work as well.
Famous microscopes manufacturers will seldom sell poor products. The test image by the 1920s Leitz microscope with its senior lenses still appears to be a little bit more crisp than that of the Tasco 1970s microscope. On the other hand you will admit that the quality difference between the Leitz and the Tasco instrument is not that big as the common quality difference to the toy microscope image.

Be careful when buying used equipment: there is a rumour that microscopes have been used as nutcrackers (!) in some laboratories.

Literature

Bruno P. Kremer: Auflösungsvermögen des Auges. Mikrokosmos 73 (1984) 91 - 93.

Links related to optical performance

Dave Walker: Counting the dots: giving microscopes a 'workout' using diatom test slides.
Martin Mach: Test diatoms - what you can expect to see even with modest optics.

The performance of small microsopes  is discussed e.g. within the following MICSCAPE articles:
The Hensoldt Tami microscope
30 grams of microscope please!
A look through an East German school microscope

© Text, images and video clips by  Martin Mach  (webmaster@baertierchen.de).
Water Bear web base is a licensed and revised version of the German language monthly magazine  Bärtierchen-Journal . Style and grammar amendments by native speakers are warmly welcomed.

Main Page